Transparent proton transport through a two-dimensional nanomesh material

Self-protecting CoFeAl-layered double hydroxides enable stable and efficient brine oxidation at 2 A cm-2

Low-energy consumption seawater electrolysis at high current density is an effective way for hydrogen production, however the continuous feeding of seawater may result in the accumulation of Cl-, leading to severe anode poisoning and corrosion, thereby compromising the activity and stability. Herein, CoFeAl layered double hydroxide anodes with excellent oxygen evolution reaction activity are synthesized and delivered stable catalytic performance for 350 hours at 2 A cm-2 in the presence of 6-fold concentrated seawater. Comprehensive analysis reveals that the Al3+ ions in electrode are etched off by OH- during oxygen evolution reaction process, resulting in M3+ vacancies that boost oxygen evolution reaction activity. Additionally, the self-originated Al(OH)n- is found to adsorb on the anode surface to improve stability. An electrode assembly based on a micropore membrane and CoFeAl layered double hydroxide electrodes operates continuously for 500 hours at 1 A cm-2, demonstrating their feasibility in brine electrolysis.

Observing Proton-Electron Mixed Conductivity in Graphdiyne

Mixed conducting materials with both ionic and electronic conductivities have gained prominence in emerging applications. However, exploring material with on-demand ionic and electronic conductivities remains challenging, primarily due to the lack of correlating macroscopic conductivity with atom-scale structure. Here, the correlation of proton-electron conductivity and atom-scale structure in graphdiyne is explored. Precisely adjusting the conjugated diynes and oxygenic functional groups in graphdiyne yields a tunable proton-electron conductivity on the order of 103. In addition, a wet-chemistry lithography technique for uniform preparation of graphdiyne on flexible substrates is provided. Utilizing the proton-electron conductivity and mechanical tolerance of graphdiyne, bimodal flexible devices serving as capacitive switches and resistive sensors are created. As a proof-of-concept, a breath-machine interface for sentence-based communication and self-nursing tasks with an accuracy of 98% is designed. This work represents an important step toward understanding the atom-scale structure-conductivity relationship and extending the applications of mixed conducting materials to assistive technology.

Fabrication of -SO3H-functionalized polyphosphazene-reinforced proton conductive matrix-mixed membranes

Proton exchange membranes (PEMs) have emerged as very promising membranes for automotive applications because of their notable proton conductivity at low temperatures. These membranes find extensive utilization in fuel cells. Several polymeric materials have been used, but their application is constrained by their expense and intricate synthetic processes. Affordable and efficient synthetic methods for polymeric materials are necessary for the widespread commercial use of PEM technology. The polymeric combination of hexachlorocyclotriphosphazene (HCCP) and 4,4-diamino-2,2-biphenyldisulfonic acid facilitated the synthesis of PP-(PhSO3H)2, a polyphosphazene with built-in -SO3H moieties. Characterization revealed that it was a porous organic polymer with high stability. PP-(PhSO3H)2 exhibited a proton conductivity of up to 8.24 × 10-2 S cm-1 (SD = ±0.031) at 353 K under 98% relative humidity (RH), which was more than two orders of magnitude higher than that of its -SO3H-free analogue, PP-(Ph)2 (2.32 × 10-4 S cm-1) (SD = ±0.019) under identical conditions. Therefore, for application in a PEM fuel cell, PP-(PhSO3H)2-based matrix-mixed membranes (PP-(PhSO3H)2-MMMs) were fabricated by mixing them with polyacrylonitrile (PAN) in various ratios. The proton conductivity could reach up to 6.11 × 10-2 S cm-1 (SD = ±0.0048) at 353 K and 98%RH, when the weight ratio of PP-(PhSO3H)2 : PAN was 3 : 1, the value of which was comparable with those of commercially available electrolytes used in PEM fuel cells. PP-(PhSO3H)2-MMM (3 : 1) had an extended lifetime of reusability. Using phosphazene and bisulfonated multiple-amine modules as precursors, we demonstrated that a porous organic polymer with a highly effective proton-conductive matrix-mixed membrane for PEM fuel cells could be produced readily by an intuitive polymeric reaction.

Bio-Inspired Subnanofluidics: Advanced Fabrication and Functionalization

Biological ion channels can realize high-speed and high-selective ion transport through the protein filter with the sub-1-nanometer channel. Inspired by biological ion channels, various kinds of artificial subnanopores, subnanochannels, and subnanoslits with improved ion selectivity and permeability are recently developed for efficient separation, energy conversion, and biosensing. This review article discusses the advanced fabrication and functionalization methods for constructing subnanofluidic pores, channels, tubes, and slits, which have shown great potential for various applications. Novel fabrication methods for producing subnanofluidics, including top-down techniques such as electron beam etching, ion irradiation, and electrochemical etching, as well as bottom-up approaches starting from advanced microporous frameworks, microporous polymers, lipid bilayer embedded subnanochannels, and stacked 2D materials are well summarized. Meanwhile, the functionalization methods of subnanochannels are discussed based on the introduction of functional groups, which are classified into direct synthesis, covalent bond modifications, and functional molecule fillings. These methods have enabled the construction of subnanochannels with precise control of structure, size, and functionality. The current progress, challenges, and future directions in the field of subnanofluidic are also discussed.

Substrate effect on charging of electrified graphene/water interfaces

Graphene, a transparent two-dimensional (2D) conductive electrode, has brought extensive new perspectives and prospects to electrochemical systems, such as chemical sensors, energy storage, and energy conversion devices. In many of these applications, graphene, supported on a substrate, is in contact with an aqueous solution. An increasing number of studies indicate that the substrate, rather than graphene, determines the organization of water in contact with graphene, i.e., the electric double layer (EDL) structure near the electrified graphene, and the wetting behavior of the graphene: the graphene sheet is transparent in terms of its supporting substrate. By applying surface-specific heterodyne-detected sum-frequency generation (HD-SFG) spectroscopy to the silicon dioxide (SiO2)-supported graphene electrode/aqueous electrolyte interface and comparing the data with those for the calcium fluoride (CaF2)-supported graphene [Y. Wang et al., Angew. Chem., Int. Ed., 2023, 62, e202216604], we discuss the impact of the different substrates on the charging of both the graphene and the substrate upon applying potentials. The SiO2-supported graphene shows pseudocapacitive behavior, consistent with the CaF2-supported graphene case, although the surface charges on SiO2 and CaF2 differ substantially. The SiO2 surface is already negatively charged at +0.57 V (vs. Pd/H2), and the negative surface charge is doubled when negative potentials are applied, in contrast with the CaF2 case, where the positive charge is reduced when negative potentials are applied. Interestingly, the charging of the graphene sheet is almost identical between the negatively charged SiO2 surface and positively charged CaF2 surface, demonstrating that the graphene charging is decoupled from the charging of the substrates.

Transition Metal Dichalcogenides Nanoscrolls: Preparation and Applications

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) nanosheets have shown extensive applications due to their excellent physical and chemical properties. However, the low light absorption efficiency limits their application in optoelectronics. By rolling up 2D TMDCs nanosheets, the one-dimensional (1D) TMDCs nanoscrolls are formed with spiral tubular structure, tunable interlayer spacing, and opening ends. Due to the increased thickness of the scroll structure, the light absorption is enhanced. Meanwhile, the rapid electron transportation is confined along the 1D structure. Therefore, the TMDCs nanoscrolls show improved optoelectronic performance compared to 2D nanosheets. In addition, the high specific surface area and active edge site from the bending strain of the basal plane make them promising materials for catalytic reaction. Thus, the TMDCs nanoscrolls have attracted intensive attention in recent years. In this review, the structure of TMDCs nanoscrolls is first demonstrated and followed by various preparation methods of the TMDCs nanoscrolls. Afterwards, the applications of TMDCs nanoscrolls in the fields of photodetection, hydrogen evolution reaction, and gas sensing are discussed.

Confinement-Controlled Water Engenders Unusually High Electrochemical Capacitance

The electrodynamics of nanoconfined water have been shown to change dramatically compared to bulk water, opening room for safe electrochemical systems. We demonstrate a nanofluidic "water-only" battery that exploits anomalously high electrolytic properties of pure water at firm confinement. The device consists of a membrane electrode assembly of carbon-based nanomaterials, forming continuously interconnected water-filled nanochannels between the separator and electrodes. The efficiency of the cell in the 1-100 nm pore size range shows a maximum energy density at 3 nm, challenging the region of the current metal-ion batteries. Our results establish the electrodynamic fundamentals of nanoconfined water and pave the way for low-cost and inherently safe energy storage solutions that are much needed in the renewable energy sector.

Subpicosecond Molecular Rearrangements Affect Local Electric Fields and Auto-Dissociation in Water

Molecular simulations of auto-dissociation of water molecules in an 81,000 atom bulk water system show that the electric field variations caused by local bond length and angle variations enhance proton transfer within ∼600 fs prior to auto-dissociation. In this paper, auto-dissociation relates to the initial separation of a proton from a water molecule to another, forming the H33O+ and OH- ions. Only transfers for which a proton's initial nearest covalently bonded oxygen remained the same for at least 1 ps prior to the transfer and for which that proton's new nearest acceptor oxygen remained the same for at least 1 ps after the transfer were evaluated. Electric fields from solvent atoms within 6 Å of a transferring proton (H*) are dominant, with little contribution from farther molecules. However, exclusion of the accepting oxygen in such electric field calculations shows that the field on H* from the other solvent atoms weakens as the time to transfer becomes less than 600 fs, indicating the primary importance of the accepting oxygen on enabling auto-dissociation. All resultant OH- and H3O+ ion pairs recombined at times greater than 1 ps after auto-dissociation. A concentration of 8.01 × 1017 cm-3 for these ion pairs was observed. The simulations indicate that transient auto-dissociation in water is more common than that inferred from dc-conductivity experiments (10-5 vs 10-7) and is consistent with the results of calculations that include nuclear quantum effects. The conductivity experiments require the rearrangement of farther water molecules to form hydrogen-bonded "water wires" that afford long-range and measurable proton transport away from the reaction site. Nonetheless, the relatively large number of picosecond-lived auto-dissociation products might be engineered within 2D layers and oriented external fields to offer new energy-related systems.

Direct Probe of Electrochemical Pseudocapacitive pH Jump at a Graphene Electrode

Molecular-level insight into interfacial water at a buried electrode interface is essential in electrochemistry, but spectroscopic probing of the interface remains challenging. Here, using surface-specific heterodyne-detected sum-frequency generation (HD-SFG) spectroscopy, we directly access the interfacial water in contact with the graphene electrode supported on calcium fluoride (CaF₂ ). We find phase transition-like variations of the HD-SFG spectra vs. applied potentials, which arises not from the charging/discharging of graphene but from the charging/discharging of the CaF₂ substrate through the pseudocapacitive process. The potential-dependent spectra are nearly identical to the pH-dependent spectra, evidencing that the pseudocapacitive behavior is associated with a substantial local pH change induced by water dissociation between the CaF₂ and graphene. Our work evidences the local molecular-level effects of pseudocapacitive charging at an electrode/aqueous electrolyte interface.

Short hydrogen-bond network confined on COF surfaces enables ultrahigh proton conductivity

The idea of spatial confinement has gained widespread interest in myriad applications. Especially, the confined short hydrogen-bond (SHB) network could afford an attractive opportunity to enable proton transfer in a nearly barrierless manner, but its practical implementation has been challenging. Herein, we report a SHB network confined on the surface of ionic covalent organic framework (COF) membranes decorated by densely and uniformly distributed hydrophilic ligands. Combined experimental and theoretical evidences have pointed to the confinement of water molecules allocated to each ligand, achieving the local enrichment of hydronium ions and the concomitant formation of SHBs in water-hydronium domains. These overlapped water-hydronium domains create an interconnected SHB network, which yields an unprecedented ultrahigh proton conductivity of 1389 mS cm⁻¹ at 90 °C, 100% relative humidity.

When hydronium ions are enriched in confined water, short hydrogen bonds (SHBs) form due to the constrained space of excess protons between pairs of water molecules. Here authors demonstrate a SHB network confined on the surface of ionic COF membranes with tunable -SO₃H groups, with proton conductivity of 1389 mS cm^-1 at 90 ^oC.

Anomalous water transport in narrow-diameter carbon nanotubes

Carbon nanotubes (CNTs) mimicking the structure of aquaporins support fast water transport, making them strong candidates for building next-generation high-performance membranes for water treatment. The diffusion and transport behavior of water through CNTs or nanoporous graphene can be fundamentally different from those of bulk water through a macroscopic tube. To date, the nanotube-length-dependent physical transport behavior of water is still largely unexplored. Herein, on the basis of molecular dynamics simulations, we show that the flow rate of water through 0.83-nm-diameter (6,6) and 0.96-nm-diameter (7,7) CNTs exhibits anomalous transport behavior, whereby the flow rate increases markedly first and then either slowly decreases or changes slightly as the CNT length l increases. The critical range of l for the flow-rate transition is 0.37 to 0.5 nm. This anomalous water transport behavior is attributed to the l-dependent mechanical stability of the transient hydrogen-bonding chain that connects water molecules inside and outside the CNTs and bypasses the CNT orifice. The results unveil a microscopic mechanism governing water transport through subnanometer tubes, which has important implications for nanofluidic manipulation.

The dielectric function profile across the water interface through surface-specific vibrational spectroscopy and simulations

The dielectric properties of interfacial water on subnanometer length scales govern chemical reactions, carrier transfer, and ion transport at interfaces. Yet, the nature of the interfacial dielectric function has remained under debate as it is challenging to access the interfacial dielectric with subnanometer resolution. Here we use the vibrational response of interfacial water molecules probed using surface-specific sum-frequency generation (SFG) spectra to obtain exquisite depth resolution. Different responses originate from water molecules at different depths and report back on the local interfacial dielectric environment via their spectral amplitudes. From experimental and simulated SFG spectra at the air/water interface, we find that the interfacial dielectric constant changes drastically across an ∼1 Å thin interfacial water region. The strong gradient of the interfacial dielectric constant leads, at charged planar interfaces, to the formation of an electric triple layer that goes beyond the standard double-layer model.

Highly Effective Proton-Conductive Matrix-Mixed Membrane Based on a -SO3H-Functionalized Polyphosphazene

A polyphosphazene with in-built -SO₃H moieties (PP-PhSO₃H) was facilely synthesized by the polymeric combination of hexachlorocyclotriphosphazene (HCCP) and sulfonate p-phenylenediamine. Characterization reveals that it is a highly stable amorphous polymer. Proton conductivity investigations showed that the synthesized PP-PhSO₃H exhibits a proton conductivity of up to 6.64 × 10^-2 S cm^-1 at 353 K and 98% relative humidity (RH). This value is almost 2 orders of magnitude higher than the corresponding value for its -SO₃H-free analogue, PP-Ph, which is 1.72 × 10^-4 S cm^-1 when measured under the same condition. Consequently, matrix-mixed membranes (labeled PP-PhSO₃H-PAN) were further prepared by mixing PP-PhSO₃H with polyacrylonitrile (PAN) in different ratios to test its potential application in the proton-exchange membrane (PEM) fuel cell. The analysis results indicate that when the weight ratio of PP-PhSO₃H/PAN is 3:1 [named PP-PhSO₃H-PAN (3:1)], its proton conductivity can reach up to 5.05 × 10^-2 S cm^-1 at 353 K and 98% RH, which is even comparable with those of proton-conductive electrolytes currently used in PEM fuel cells. Furthermore, the continuous test demonstrates that the PP-PhSO₃H-PAN (3:1) has long-life reusability. This research reveals that by using phosphazene and sulfonated multiple-amine modules as precursors, organic polymers with excellent proton conductivity for the assembly of matrix-mixed membranes in PEM fuel cells can be easily synthesized by a simple polymeric process.

Facile construction of a highly proton-conductive matrix-mixed membrane based on a -SO3H functionalized polyamide

Developing a facile strategy to construct low-cost and efficient proton-conductive electrolytes is pivotal in the practical application of proton exchange membrane (PEM) fuel cells. Herein, a polyamide with in-built -SO₃H moieties, PA(PhSO3H)2, was synthesized via a simple one-pot polymeric acylation process. Investigations via electrochemical impedance spectroscopy (EIS) measurements revealed that the fabricated PA(PhSO3H)2 displays a proton conductivity of up to 5.54 × 10^-2 S cm^-1 at 353 K under 98% relative humidity (RH), which is more than 2 orders of magnitude higher than that of its -SO₃H-free analogue PA(Ph)2 (2.38 × 10^-4 S cm^-1) under the same conditions. Therefore, after mixing with polyacrylonitrile (PAN) at different ratios, PA(PhSO3H)2-based matrix-mixed membranes were subsequently made and the analysis results revealed that the proton conductivity can reach up to 5.82 × 10^-2 S cm^-1 at 353 K and 98% RH when the weight ratio of PA(PhSO3H)2 : PAN is in 3 : 1 (labeled as PA(PhSO3H)2-PAN(3 : 1)), the value of which is comparable even to those of commercially available electrolytes that are used in PEM fuel cells. In addition, continuous testing shows that PA(PhSO3H)2-PAN(3 : 1) possesses long-life reusability. This work demonstrates that, utilizing the simple reaction of polymeric acylation with a sulfonated module as a precursor, highly effective proton-conductive membranes for PEM fuel cells can be achieved in a facile manner.

Highly Effective Proton-Conduction Matrix-Mixed Membrane Derived from an -SO3H Functionalized Polyamide

Developing a low-cost and effective proton-conductive electrolyte to meet the requirements of the large-scale manufacturing of proton exchange membrane (PEM) fuel cells is of great significance in progressing towards the upcoming “hydrogen economy” society. Herein, utilizing the one-pot acylation polymeric combination of acyl chloride and amine precursors, a polyamide with in-built -SO₃H moieties (PA-PhSO₃H) was facilely synthesized. Characterization shows that it possesses a porous feature and a high stability at the practical operating conditions of PEM fuel cells. Investigations of electrochemical impedance spectroscopy (EIS) measurements revealed that the fabricated PA-PhSO₃H displays a proton conductivity of up to 8.85 × 10⁻² S·cm⁻¹ at 353 K under 98% relative humidity (RH), which is more than two orders of magnitude higher than that of its -SO₃H-free analogue, PA-Ph (6.30 × 10⁻⁴ S·cm⁻¹), under the same conditions. Therefore, matrix-mixed membranes were fabricated by mixing with polyacrylonitrile (PAN) in different ratios, and the EIS analyses revealed that its proton conductivity can reach up to 4.90 × 10⁻² S·cm⁻¹ at 353 K and a 98% relative humidity (RH) when the weight ratio of PA-PhSO₃H:PAN is 3:1 (labeled as PA-PhSO₃H-PAN (3:1)), the value of which is even comparable with those of commercial-available electrolytes being used in PEM fuel cells. Additionally, continuous tests showed that PA-PhSO₃H-PAN (3:1) possesses a long-life reusability. This work demonstrates, using the simple acylation reaction with the sulfonated module as precursor, that low-cost and highly effective proton-conductive electrolytes for PEM fuel cells can be facilely achieved.

Angstrom-scale ion channels towards single-ion selectivity

Artificial ion channels with ion permeability and selectivity comparable to their biological counterparts are highly desired for efficient separation, biosensing, and energy conversion technologies. In the past two decades, both nanoscale and sub-nanoscale ion channels have been successfully fabricated to mimic biological ion channels. Although nanoscale ion channels have achieved intelligent gating and rectification properties, they cannot realize high ion selectivity, especially single-ion selectivity. Artificial angstrom-sized ion channels with narrow pore sizes <1 nm and well-defined pore structures mimicking biological channels have accomplished high ion conductivity and single-ion selectivity. This review comprehensively summarizes the research progress in the rational design and synthesis of artificial subnanometer-sized ion channels with zero-dimensional to three-dimensional pore structures. Then we discuss cation/anion, mono-/di-valent cation, mono-/di-valent anion, and single-ion selectivities of the synthetic ion channels and highlight their potential applications in high-efficiency ion separation, energy conversion, and biological therapeutics. The gaps of single-ion selectivity between artificial and natural channels and the connections between ion selectivity and permeability of synthetic ion channels are covered. Finally, the challenges that need to be addressed in this research field and the perspective of angstrom-scale ion channels are discussed.

One-Atom-Thick Crystals as Emerging Proton Sieves

Two-dimensional (2D) crystals, despite their atomic thickness, have long been considered as impermeable membranes to all molecules and atoms under ambient conditions: even the smallest of atoms, hydrogen, is expected to take billions of years to penetrate the 2D lattice covered with dense electron clouds. Recently it has been found that monolayer graphene, hexagonal boron nitride, and some other one-atom-thick crystals are highly permeable to protons, raising fundamental questions about the details of the transport process. In this Perspective, we review the mechanism of proton transport through 2D crystals and the related room-temperature quantum effects; the potential applications of 2D membranes in proton-related separation and sieving techniques, including proton exchange membranes and hydrogen isotope separation; and factors that enhance proton permeation and in turn influence 2D membrane design.

Tight Covalent Organic Framework Membranes for Efficient Anion Transport via Molecular Precursor Engineering

Fabricating covalent organic frameworks (COFs) membranes with tight structure, which can fully utilize well-defined framework structure and thus achieve superior conduction performance, remains a grand challenge. Herein, through molecular precursor engineering of COFs, we reported the fabrication of tight COFs membrane with the ever-reported highest hydroxide ion conductivity over 200 mS cm^-1 at 80 °C, 100 % RH. Six quaternary ammonium-functionalized COFs were synthesized by assembling functional hydrazides and different aldehyde precursors. In an organic-aqueous reaction system, the impact of the aldehyde precursors with different size, electrophilicity and hydrophilicity on the reaction-diffusion process for fabricating COFs membranes was elucidated. Particularly, more hydrophilic aldehydes were prone to push the reaction zone from the interface region to the aqueous phase of the reaction system, the tight membranes were thus fabricated via phase-transfer polymerization process, conferring around 4-8 times the anion conductivity over the loose membranes via interfacial polymerization process.

High Enhancement in Proton Conductivity by Incorporating Sulfonic Acids into a Zirconium-Based Metal-Organic Framework via "Click" Reaction

Taking a robust zirconium-based metal-organic framework, UiO-66, as a prototype, functional postmodification via the versatile Cu(I)-catalyzed azide-alkyne "click" reaction was carried out, and sulfonic acid groups were successfully grafted into its skeleton. Characterizations revealed that the MOF network was still well maintained after being treated by "clicked" modification. Investigations by electrochemical impedance spectroscopy measurements revealed that its proton conductivity increases exponentially up to 8.8 × 10^-3 S cm^-1 at 80 °C and 98% RH, while those of the UiO-66 and UiO-66-NH₂ are only 6.3 × 10^-6 and 3.5 × 10^-6 S cm^-1, respectively, at the same condition. Additionally, the continuous test shows it possesses long-life reusability. Such a remarkable enhancement on the proton conductivities and high performance in long-life reusability of the resultant MOF demonstrated that the "click" reaction is a facile reaction in postmodification of robust porous materials toward targeted applications, with which highly promising candidates of proton-conductive electrolytes for applying in proton-exchange-membrane (PEM) fuel cell can be achieved.

Biomimetic N-Doped Graphene Membrane for Proton Exchange Membranes

Proton exchange membranes (PEMs) with both high selectivity and high permeance are of great demand in hydrogen-based applications, especially in fuel cells. Although graphene membranes have shown high selectivity of protons over other ions and molecules, the relatively low permeance of protons through perfect pristine graphene restricts its practical applications. Inspired by the nitrogen-assisted proton transport in biological systems, we introduced N-doping to increase the proton permeance and proposed a type of N-doped graphene membranes (NGMs) for proton exchange, which have both high proton permeance and high selectivity. Compared to the state-of-the-art commercial PEMs, the NGMs show significant increases in both areal proton conductivity (2-3 orders of magnitude) and selectivity of proton to methanol (1-2 orders of magnitude). The work realized the controllable tuning of proton permeance of the graphene membrane with N-doping and developed a new type of graphene-based PEMs with high performance for practical applications.

Nanomeshes with Sub-10 nm Pores by Glycerol-Triggered 2D Assembly in Liquid Phases for Fast and Selective Membranes

Nanomeshes having ultrathin thicknesses and penetrating nanopores promise fast diffusion and precise selectivity and are highly desired in diffusion-involved processes such as separation. Herein, we report a liquid-phase two-dimensional (2D) assembly strategy to synthesize phenolic and carbonaceous nanomeshes with sub-10 nm pores and thicknesses. The synthesis is enabled simply by introducing glycerol in the thermopolymerization of resol/polyether micelles dispersed in ethanol. Experimental and simulation results reveal that glycerol's strong ability to form hydrogen bonds constrain the motion of the micelles, directing them to pack and merge exclusively in the lateral direction. Upon removal of polyether, we obtain phenolic nanomeshes with lateral sizes up to hundreds of micrometers, which can be further converted to carbonaceous nanomeshes. As a proof of concept, we use stacked phenolic and carbonaceous nanomeshes as separation membranes. They show superior permselectivity to nanosized solutes with permeance ∼2-110 times higher than that of other membranes.

Facile Fabrication of Subnanopores in Graphene under Ion Irradiation: Molecular Dynamics Simulations

Two-dimensional (2D) nanoporous membranes have attracted great interest in water desalination, energy conversion, electrode, and gas separation. The performances of these membranes are mainly determined by the nanopores, and only with satisfactory subnanometer pores can applications such as high-precision ion separation be realized. Therefore, to efficiently create subnanopores in 2D materials is of great importance. Here, using molecular dynamics simulations, we demonstrate that the direct irradiation of energetic ion is capable of introducing subnanopores in monolayer graphene. By changing the energy of the incident Au ion, the averaged pore diameter can be adjusted from 4.2 to 5.6 Å, and pore diameter distributions are narrow. In the formation processes of the subnanopores, the cascade collisions caused by the primary knock-on atom (PKA) predominates, and pores can only be created in ion impact positions close to the PKA, especially for the incident ion with high energy. Our results show the promise of ion irradiation as a facile method to fabricate subnanopores in 2D materials. As hydrated ions, gases, and small organic molecules have diameters of several angstroms, close to the pore sizes, the created nanoporous membranes can be used to separate those matter, which is conducive to accelerating related applications.